/**
 * Alipay.com Inc.
 * Copyright (c) 2004-2014 All Rights Reserved.
 */
package cn.youcredit.thread.common.service.zmApi.internal.util;

/**
 * @author xiaoqing.zhouxq
 * @version $Id: Base64Util.java, v 0.1 2015年4月27日 上午11:07:55 xiaoqing.zhouxq
 *          Exp $
 */
public class Base64Util extends CoderUtil {
    /**
     * Translates the specified byte array into a Base64 string as per
     * Preferences.put(byte[]).
     *
     * @param a
     * @return
     */
    public static String byteArrayToBase64(byte[] a) {
        return Base64Util.byteArrayToBase64(a, false);
    }

    /**
     * Translates the specified byte array into an "alternate representation"
     * Base64 string. This non-standard variant
     * uses an alphabet that does not contain the uppercase alphabetic
     * characters, which makes it suitable for use in
     * situations where case-folding occurs.
     *
     * @param a
     * @return
     */
    public static String byteArrayToAltBase64(byte[] a) {
        return Base64Util.byteArrayToBase64(a, true);
    }

    private static String byteArrayToBase64(byte[] a, boolean alternate) {
        int aLen = a.length;
        int numFullGroups = aLen / 3;
        int numBytesInPartialGroup = aLen - 3 * numFullGroups;
        int resultLen = 4 * ((aLen + 2) / 3);
        StringBuffer result = new StringBuffer(resultLen);
        char[] intToAlpha = alternate ? Base64Util.intToAltBase64
            : Base64Util.intToBase64;

        // Translate all full groups from byte array elements to Base64
        int inCursor = 0;
        for (int i = 0; i < numFullGroups; i++) {
            int byte0 = a[inCursor++] & 0xff;
            int byte1 = a[inCursor++] & 0xff;
            int byte2 = a[inCursor++] & 0xff;
            result.append(intToAlpha[byte0 >> 2]);
            result.append(intToAlpha[byte0 << 4 & 0x3f | byte1 >> 4]);
            result.append(intToAlpha[byte1 << 2 & 0x3f | byte2 >> 6]);
            result.append(intToAlpha[byte2 & 0x3f]);
        }

        // Translate partial group if present
        if (numBytesInPartialGroup != 0) {
            int byte0 = a[inCursor++] & 0xff;
            result.append(intToAlpha[byte0 >> 2]);
            if (numBytesInPartialGroup == 1) {
                result.append(intToAlpha[byte0 << 4 & 0x3f]);
                result.append("==");
            } else {
                // assert numBytesInPartialGroup == 2;
                int byte1 = a[inCursor++] & 0xff;
                result.append(intToAlpha[byte0 << 4 & 0x3f | byte1 >> 4]);
                result.append(intToAlpha[byte1 << 2 & 0x3f]);
                result.append('=');
            }
        }
        // assert inCursor == a.length;
        // assert result.length() == resultLen;
        return result.toString();
    }

    /**
     * This array is a lookup table that translates 6-bit positive integer index
     * values into their "Base64 Alphabet"
     * equivalents as specified in Table 1 of RFC 2045.
     */
    private static final char intToBase64[] = { 'A', 'B', 'C', 'D', 'E', 'F',
        'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T',
        'U', 'V', 'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h',
        'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v',
        'w', 'x', 'y', 'z', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
        '+', '/' };

    /**
     * This array is a lookup table that translates 6-bit positive integer index
     * values into their
     * "Alternate Base64 Alphabet" equivalents. This is NOT the real Base64
     * Alphabet as per in Table 1 of RFC 2045. This
     * alternate alphabet does not use the capital letters. It is designed for
     * use in environments where "case folding"
     * occurs.
     */
    private static final char intToAltBase64[] = { '!', '"', '#', '$', '%',
        '&', '\'', '(', ')', ',', '-', '.', ':', ';', '<', '>', '@', '[', ']',
        '^', '`', '_', '{', '|', '}', '~', 'a', 'b', 'c', 'd', 'e', 'f', 'g',
        'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u',
        'v', 'w', 'x', 'y', 'z', '0', '1', '2', '3', '4', '5', '6', '7', '8',
        '9', '+', '?' };

    /**
     * Translates the specified Base64 string (as per Preferences.get(byte[]))
     * into a byte array.
     *
     * @param s
     * @return
     * @throw IllegalArgumentException if <tt>s</tt> is not a valid Base64
     *        string.
     */
    public static byte[] base64ToByteArray(String s) {
        return Base64Util.base64ToByteArray(s, false);
    }

    /**
     * Translates the specified "alternate representation" Base64 string into a
     * byte array.
     * 
     * @param s
     * @return
     * @throw IllegalArgumentException or ArrayOutOfBoundsException if <tt>s</tt>
     *        is not a valid alternate
     *        representation Base64 string.
     */
    public static byte[] altBase64ToByteArray(String s) {
        return Base64Util.base64ToByteArray(s, true);
    }

    private static byte[] base64ToByteArray(String s, boolean alternate) {
        byte[] alphaToInt = alternate ? Base64Util.altBase64ToInt
            : Base64Util.base64ToInt;
        int sLen = s.length();
        int numGroups = sLen / 4;
        if (4 * numGroups != sLen) {
            throw new IllegalArgumentException(
                "String length must be a multiple of four.");
        }
        int missingBytesInLastGroup = 0;
        int numFullGroups = numGroups;
        if (sLen != 0) {
            if (s.charAt(sLen - 1) == '=') {
                missingBytesInLastGroup++;
                numFullGroups--;
            }
            if (s.charAt(sLen - 2) == '=') {
                missingBytesInLastGroup++;
            }
        }
        byte[] result = new byte[3 * numGroups - missingBytesInLastGroup];

        // Translate all full groups from base64 to byte array elements
        int inCursor = 0, outCursor = 0;
        for (int i = 0; i < numFullGroups; i++) {
            int ch0 = Base64Util.base64toInt(s.charAt(inCursor++), alphaToInt);
            int ch1 = Base64Util.base64toInt(s.charAt(inCursor++), alphaToInt);
            int ch2 = Base64Util.base64toInt(s.charAt(inCursor++), alphaToInt);
            int ch3 = Base64Util.base64toInt(s.charAt(inCursor++), alphaToInt);
            result[outCursor++] = (byte) (ch0 << 2 | ch1 >> 4);
            result[outCursor++] = (byte) (ch1 << 4 | ch2 >> 2);
            result[outCursor++] = (byte) (ch2 << 6 | ch3);
        }

        // Translate partial group, if present
        if (missingBytesInLastGroup != 0) {
            int ch0 = Base64Util.base64toInt(s.charAt(inCursor++), alphaToInt);
            int ch1 = Base64Util.base64toInt(s.charAt(inCursor++), alphaToInt);
            result[outCursor++] = (byte) (ch0 << 2 | ch1 >> 4);

            if (missingBytesInLastGroup == 1) {
                int ch2 = Base64Util.base64toInt(s.charAt(inCursor++),
                    alphaToInt);
                result[outCursor++] = (byte) (ch1 << 4 | ch2 >> 2);
            }
        }
        // assert inCursor == s.length()-missingBytesInLastGroup;
        // assert outCursor == result.length;
        return result;
    }

    /**
     * Translates the specified character, which is assumed to be in the
     * "Base 64 Alphabet" into its equivalent 6-bit
     * positive integer.
     *
     * @throw IllegalArgumentException or ArrayOutOfBoundsException if c is not
     *        in the Base64 Alphabet.
     */
    private static int base64toInt(char c, byte[] alphaToInt) {
        int result = alphaToInt[c];
        if (result < 0) {
            throw new IllegalArgumentException("Illegal character " + c);
        }
        return result;
    }

    /**
     * This array is a lookup table that translates unicode characters drawn
     * from the "Base64 Alphabet" (as specified in
     * Table 1 of RFC 2045) into their 6-bit positive integer equivalents.
     * Characters that are not in the Base64
     * alphabet but fall within the bounds of the array are translated to -1.
     */
    private static final byte base64ToInt[] = { -1, -1, -1, -1, -1, -1, -1, -1,
        -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
        -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 62,
        -1, -1, -1, 63, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -1,
        -1, -1, -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16,
        17, 18, 19, 20, 21, 22, 23, 24, 25, -1, -1, -1, -1, -1, -1, 26, 27, 28,
        29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46,
        47, 48, 49, 50, 51 };

    /**
     * This array is the analogue of base64ToInt, but for the nonstandard
     * variant that avoids the use of uppercase
     * alphabetic characters.
     */
    private static final byte altBase64ToInt[] = { -1, -1, -1, -1, -1, -1, -1,
        -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
        -1, -1, -1, -1, -1, -1, -1, -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, -1, 62, 9,
        10, 11, -1, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 12, 13, 14, -1, 15,
        63, 16, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
        -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 17, -1, 18, 19, 21, 20, 26, 27,
        28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45,
        46, 47, 48, 49, 50, 51, 22, 23, 24, 25 };
}
